Groundwater levels update (3 February)

Over recent weeks, scientists from the Environment Agency (EA) and BGS have been keeping a close eye on groundwater levels, monitoring the response of aquifers to the heavy rainfall experienced in parts of the country in December 2015 and January 2016.

In the last week of January 2016 there was more rainfall in areas where groundwater levels were already high, but, although water levels rose, they did not generally reach the levels at which significant groundwater flooding may occur, and some levels are now declining. Groundwater flood alerts are still in place in areas of some southern counties of England, but the impact on properties and infrastructure has been limited.

Although the immediate risk of groundwater flooding is reducing, we remain in a situation where groundwater levels are relatively high and superficial aquifers (comprising relatively shallow, unconsolidated deposits) will be saturated. This means that further periods of intense or prolonged rainfall could potentially lead to more localised groundwater flooding.

Figure 1: January 2016 rainfall amount per cent of 1981–2010 average. Contains public sector information licensed under the Open Government Licence v1.0.

Figure 2: January 2016 rainfall amount actual value. Contains public sector information licensed under the Open Government Licence v1.0.

South east England

Figure 3: hydrograph for Chilgrove House, north of Chichester, in the unconfined Chalk. Red circle highlights the area of the graph described in the text. Purple line shows start of 2016.

The south east of England received up to >200 per cent of average January rainfall (Figure 1). Rainfall across the area from Eastbourne to Weymouth was mostly in the range of 150–200 mm (Figure 2).

The monitoring well at Chilgrove House is used to observe groundwater levels in the unconfined Chalk aquifer of West Sussex. Since the start of 2016, the groundwater level here rose to a peak of about 75.4 m, fell a few metres and then rose again in response to further rainfall (Figure 3). The water level in this well appears to be starting to fall again as of the morning of 3 February 2016.

Yorkshire Chalk

The Yorkshire Chalk has seen below average rainfall in January (Figure 2). The groundwater level at Wetwang (in the unconfined Chalk) has responded to this and fallen by over 2.5 m since it peaked about 19 January 2016 (Figure 4). The less responsive confined Chalk is illustrated by Dalton Holme, where the groundwater level is still rising in response to the earlier rainfall (Figure 4).

Data notes and acknowledgement

Hydrograph data note: data up until the end of December 2015 are from the National Groundwater Level Archive (NGLA), and have been quality assured prior to submission, whereas January and February 2016 data are derived directly from the EA's telemetered boreholes and have not yet been quality assured.